For Chemical Operators: 3 Reasons to Use 80 GHz Radar for Liquid Level Measurement

In applications measuring harsh, caustic chemicals, many operators separate their level detectors from the process via a ball valve. This is a common practice and frankly, a smart move. External access allows the user to keep the process moving during maintenance work or when replacing a faulty sensor. You can also look at the wisdom of mounting a level instrument on a ball valve this way: If a problem arises with an instrument inside of a tank, that particular tank—or worse, an entire line—might have to be shut down, potentially leading to thousands of dollars in lost production. That’s a bad day at work. Many plants choose to play it safe and mount sensors on a ball valve. 

Pairing a ball valve with a 26 GHz radar sensor has a history of difficulty because the interior surfaces of the valve reflect radar signals back to the sensor, creating an excess of signal noise at the top of the measurement.  Similar noise is created when mounting a 26 GHz radar instrument on a tall nozzle, as reflections from the nozzle’s narrow walls reflect back to the sensor antenna.

80 GHz radar technology presents chemical-industry users new option for liquid level measurement, even when a sensor is mounted on a ball valve or a nozzle. These higher-frequency sensors emit a radar beam as narrow as 3°, so a smaller portion of the signals contact the valve or nozzle walls, minimizing noise and creating an easier experience for users who now have a clear picture of the level inside a tank. 80 GHz radar sensors have been installed successfully on a broad range of 3-in. and 4-in. ball valves and on nozzles as tall as 5 feet.  

I’d guess that everyone who works in chemical processing has struggled to accurately measure a liquid with low dielectric constant (dK). These unreflective products demand a highly-sensitive measurement device to detect the weak signals they return to the antenna. In the past, if a liquid’s dielectric constant was too low, radar might not be sensitive enough to measure it. That’s changed due to advancements in dynamic range.

Measured in decibels (dB), dynamic range is an indicator of sensitivity. The larger the dynamic range of a radar sensor, the smaller the signals it can measure. VEGA’s 80 GHz radar for liquid level, the VEGAPULS 64, has a dynamic range of 120 dB, large enough to measure any liquid chemical regardless of dK value—dielectric constant isn’t even part of the conversation anymore, and 80 GHz radar is compatible with any liquid chemical.

Portal windows on process vessels are familiar sights in the chemical industry. Historically, users have installed these portholes to visually check the level, ensure mixes are reacting properly, and confirm everything looks as it should. 

Vessels with windows permit users to measure liquid level in a unique way: by mounting a radar sensor above the glass. Radar microwaves penetrate the glass, reach the product inside, and reflect through the glass back to the sensor. This eliminates two major expenses because users are spared from retrofitting a tank to accommodate a sensor and can continue running a process during installation. Functionally, nothing changes as users can simply move the sensor for a moment to look through the glass and see what’s happening inside a vessel. 

As a matter of disclosure, you should know that this isn’t new. Any radar sensor can measure liquid level through glass, but the ease and clarity of this measurement is new and is made possible by 80 GHz transmission frequency. Windows are often welded, bolted, or clamped directly onto a tank wall or roof with a circular flange, while others are mounted on a nozzle. As is the case with ball valves and nozzles, the sides of the flange reflect signals to the antenna and create noise. The interference forces operators to leave empty space inside a tank to make a clear distinction between the signal received from the vessel and the signal received from the product. 

Further complicating the use of last-generation, 26 GHz sensors above such vessels is the fact that most windows are installed at a natural slope in the tank. This angle narrows the path to the liquid, increasing the degree of difficulty in setting up a sensor so the beam is perpendicular to the product. Perpendicularity is important because it’s in direct relationship to the strength of the signal the sensor receives. In order to minimize the small signals that bounce from the angled window back to the sensor, it’s recommended that users pair a 26 GHz radar sensor with a window installed at least a 30° angle. This forces users to choose between a strong signal from the product accompanied by reflections from the glass or a weak signal from the product and no reflections from the glass. Call that the curse of bad choices.

80 GHz radar sensors solve the problems signal noise and narrow paths create because of signal focusing. Installed above any window installed at a 5-10° angle, the narrow radar beam misses the sides of the flange and travels a tight path to the product without sacrificing signal strength.

There’s no magic bullet for level measurement of liquid chemicals; even 80 GHz radar sensors aren’t the optimal choice under certain conditions. Heavy foam traps microwave signals and prevents them from returning to a radar antenna, so in such applications it is recommended users turn to guided wave radar. Radiation-based technology may be better suited for measuring level of highly toxic, chemically-aggressive liquids, and electronic differential pressure is a popular choice for measuring liquid gas level. Operators should contact their instrumentation manufacturer for advice about selecting the right measurement technology for their needs.

Each chemical process has its own demands and idiosyncrasies and it would be dishonest to say that one technology is the best fit for every liquid level application. But with 80 GHz radar available, we’re nearer to that point than we were just two years ago. Given its focus, which allows it to deliver clear measurements when mounted on valves and nozzles, its large dynamic range, which allows it to measure low-dK liquid, and its ability to measure through portal windows and plastic tanks, end-users and engineers in chemical plants should consider 80 GHz radar as the first choice in all liquid level applications.